The present invention relates generally to electrochemical cells, and in particular, it relates to the junction structure of electrochemical cells.
Ion concentrations of solutions are typically measured through the use of an ion sensing electrode in connection with a reference electrode or cell. The potential difference between the two electrodes is a function of the concentration of the ion in the solution being sensed. A common example is the measurement of pH in aqueous solutions in which a pair of electrodes is used to measure the hydrogen ion concentration and a pH meter provides the instrumentation that indicates the quantitative value.
Reference cells ordinarily include a salt solution disposed within a chamber, an electrode within the salt solution, and a junction which provides an ionic connection between the salt solution of the reference electrode and the solution being sampled.
The liquid junctions of the prior art reference electrodes have been constructed to permit leakage, that is fluid flow between the reference salt solution and the sampling solution. Such junctions have included agar gel connections, wicks, asbestos fibers, small capillary tubes, glass tubes with cracks therein, sintered glass plugs sealed in glass tubes, annular passages provided between solid metal rods and the walls of the tubes, porous ceramic rods, sintered plastic rods, and ground glass sleeves.
More recently, the Neti et al U.S. Pat. No. 4,002,547 describes the use of a relatively strong, electrochemically inactive salt distributed through a hydrophobic polymer. The salt is incorporated into the polymer prior to molding and thereafter the polymeric bar stock is sintered to form the reference electrode housing.
In an increasing number of applications, liquid flow or leakage between the reference solution and the sampling solution present problems. For example, care must be taken to minimize loss of the reference solution due to temperature or pressure extremes since such extremes will force the solution from the cell decreasing the life of the cell or destabilizing the cell. In addition, the reference cell can become contaminated by leakage of the sample solution into the cell. This leakage can cause dilution of the reference solution and/or can poison the cell.
In many applications, there are strict sanitary requirements which make the seals of the prior art reference electrodes unacceptable. Such sanitary requirements do not permit sealing mechanisms such as a typical 0-ring and groove that are found in prior art reference electrodes. In addition, prior art junctions which permit (leak) fluid into and out of the cell may compromise sanitary conditions.
Lastly, liquid junctions add greatly to the cell's costs due to the additional parts needed to form the junction and the labor involved in providing the junction.